Tapping device



L 1951i c. E. SPRAGUH gssv TAPPING DEVICE Filed sepi. 29, 1947 HHH! IVI /4 Tram/MEW Patented May 1, 1951 UNITED STATES 'rsNr OFFICE 1 Claim.

This invention relates generally to the tapping of holes with power-driven tools and particularly to a tapping device.

The main object of this invention is to provide a means for frictionally holding a tap in a thread-cutting direction and positively holding it in a withdrawing direction.

The second object is to reduce the breakage of taps and to avoid the necessity of close observance of the operation to insure the completion of the threading operation without danger of an abnormal load breaking the tap.

I accomplish these and other objects in the manner set forth in the following specification as illustrated in the accompanying drawing, in which:

Fig. l is a longitudinal section through the device.

Fig. 2 is a tranverse section taken along the line 2 2 in Fig. l.

Fig. 3 is a transverse section taken along the line 3-3 in Fig. l.

Fig. 4 is a section taken along the line 4-4 in Fig. 2.

Fig. 5 is a perspective View of the wedge element.

Similar numbers of reference refer to the same or similar parts throughout the several views.

Referring in detail to the drawing, there is shown a piece of work I which is held in the work holder of a tapping machine such as is now in common use in which the work is turned in either direction under power and control 'of the machine (not shown) While the tap II is relatively still except that it is advanced to be held frictionally while thread cutting, but to be held positively when backing out of the thread. It is thisI feature which forms the basis of the present invention.

There is shown a support I2 for a tapping spindle I3 which is held against rotation by means of a key I4.

On the spindle I3 is formed a cylindrical housing I5 within which is threaded a bearing I6 for the cylindrical portion I1 of the tap holding chuck IB in whose head I9 is held a tap supporting collet by means of a set screw 2|. The shank 22 is provided with a square end 23 which is held between the four screws 24 extending into the chuck I8 and held by the lock nuts 25. On the portion I1 is formed an enlarged end 26 having a V groove 21 formed therein which is occupied by the friction dog 28 which is secured to the housing I5 by means The cross section of the dog The of the screws 29. 28 is the same as that of the groove 21. dog 23 is longitudinally curved as shown.

Tangential to the groove 21 is the locking dog 3E) which is slidable in the auxiliary housing 3l formed on the housing I5.

The dog 30 is provided with a reduced shank 32 which receives the compression spring 33 mounted on the pin 3x1 within the adjusting cap 35 which is screwed onto the threaded end 36 of the housing 3|.

It will be noted that the dog 30 is flattened to form a xl-shaped wedge whose small end 31 iits the groove 21, that is, the faces 38 will Wedge into the groove 21 under the urging of the spring 33.

The operation of the device is as follows:

Assuming that a thread is to be cut in the hole 39 of the work I 0 and that the work is being revolved by suitable power and moved toward the stationary tap II. As the tap begins to cut its thread it is held against rotation by the friction between the dog 28 and the groove 2-1 as set up by the end thrust from the tap II. If the tap should bottom before the rotation of the work I0 is reversed (either manually or automatically as the case may be) or an abnormal resistance be offered to the cutting operation, then the tap I I will yield to the rotation cf the work Il), thereby protecting the tap against breakage. f

Whenv the rotation of the Work IIJ is reversed, the dog 33 is wedged into the groove 21 due to the friction plus the action of the spring 33, producing a positive holding action for the tap II while it is being withdrawn.

It will be understood that the collet 20 may be replaced by a button die or solid type die without departing from the spirit of this invention.

I am, of course, aware that numerous forms of tapping devices have been constructed in the past. I, therefore, do not claim such devices broadly but I do intend to cover such forms and modications thereof as fall fairly Within the appended claim.

I claim:

A tapping device having in combination a housing adapted to be held in the turret of a tapping machine, said housing having a cylindrical interior, a tap holding chuck journalling in said housing, said chuck having a V-groove formed around same, said chuck having a limited endwise motion with relation to said housing, an arcuate shoe in said groove secured to said housing, a wedge slidably mounted in said housing tangentially with relation to said groove, a spring for urging said wedge into engagement with the sides of said groove, the holding action between said housing and chuck in a tapping direction being due to the friction between said shoe and one side of the groove, and the holding action between said housing and chuck in a tap withdrawing direction consisting of the friction on one side of' the arcuate shoe plus the total friction between said wedge and both sides of said groove.

CHESTER E. SPRAGUE.

REFERENCES CITED- The following references areV of record. in the file of this patenti Number Number 4 UNITED STATES PATENTS Name Date Nelson June 27, 1893 Douglas Mar. 16, 1909 Huling Mar. 8, 1910 Rogers May 9, 1911 Nace Nov. 23, 1926 Dawler June 3, 1941 FOREIGN PATENTS Country Date Great Britain May 12, 1910 Great Britain Nov. 14, 1918 

